Britain's security services are set to clash with Parliament and the country's powerful press over revelations that police secretly used a controversial law to identify journalists' sources, triggering a wider debate about media freedom in the digital age.

Detectives used a law usually reserved for terror suspects to find out the sources for scoops in The Sun and the Mail on Sunday that led to the downfall of two senior officials.

Other cases have since emerged, although the full scale of the practice is unknown since police do not need to go through a court under the Regulation of Investigatory Powers Act.

In the case of The Sun, the phone records of political editor Tom Newton Dunn were accessed to find out which officers were behind allegations that Andrew Mitchell, the government's senior representative in Parliament, swore at police.

The newspaper had used the material in a front-page story.

"It was a fairly simple process for them to identify which telephone numbers could be linked to police officers," said Dominic Ponsford from the Press Gazette trade magazine, which is running a "Save Our Sources" campaign.

'Nobody above law'

RIPA was introduced in 2000 to take account of advances in technology and to comply with European law and specifies when authorities can access communications.

But a legal challenge has now been launched in the European Court of Human Rights on behalf of the Bureau of Investigative Journalism, which claims that the law is being used in a way that contravenes the right to free speech.

"There has been a huge amount of case law at the European Court to say that as part of the right to freedom of expression, the confidentiality of journalist sources has the highest possible protection in law," Ponsford said.

But Metropolitan Police assistant commissioner Mark Rowley insisted the force would continue to use the law.

"Nobody should be above the law, whether it's a member of the public, whether it's a police officer, whether it's a journalist," he told the BBC.

The country's newspapers boast of a tradition of holding institutions to account, but now complain that their huge resources and technical know-how are making it an uneven battleground.

"Journalists must remain arrows and not the target," Seamus Dooley, secretary of Ireland's National Union of Journalists, recently told a conference on journalism in the age of mass surveillance, hosted at The Guardian newspaper's London headquarters.

"The message must be: we are watching Big Brother," he added.

(China Daily 11/01/2014 page11)